#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>

int sum(int x)
{
    if (x < 3)
        return 1;
    else
        return sum(x - 1) + sum(x - 2);
}
int main() {
    int n = 0;
    scanf("%d", &n);
    int t = sum(n);
    printf("%d", t);
    return 0;
}